Diesel oil or gasoline engines are widely used power sources for rotating the blade of a power mower. As is generally known, because the noise generated during operation of the engine is big, mowing is often restricted to a stipulated period of time in residential areas. Despite this, the noise generated by the engine is still very disturbing.
Some nations have grave concern about the disturbing noise caused by power mowers. Some have even made laws to prohibit use of power mowers in residential areas.
At present, the only device to replace the power mower is one that utilizes a conventional motor that is mounted on the lawn mower, in which a rotary shaft of the motor is directly linked to the shaft of the mower's blade to drive the blade. The rotary torque required by the blade during mowing comes from the rotary shaft of the motor. The rotary shaft is driven by a rotor located in the central portion of the motor. As a general rule, the rotor has a plurality of coils which, when electric currents are conducted therethrough, will generate an electromagnetic field in cooperation with a plurality of magnets on the housing of the motor. The electromagnetic field thus generated rotates the rotor and the rotary shaft. Nonetheless, the rotary shaft that transmits the power has a limited diameter. Therefore, the inertia generated during rotation of the rotor and the rotary shaft is limited. In addition, when the blade of the lawn mower operates, it will periodically reduce its rotational speed upon contact with the grass stalks, resulting in the rise in coil resistance on the rotor so that the coils become heated. The heat generated by the coils in the motor is difficult to dissipate.
Hence, if the conventional motor is directly used to provide power for the blade of the lawn mower, consumption of electric power will be greatly increased due to the rise in coil resistance. Batteries are, therefore, not suitable as a power source. In other words, a lawn mower using the conventional motor as a power source has to be equipped with very long electric wires. Consequently, the mower will increase in weight; its construction will be more complicated; and it will be inconvenient to operate or move the mower. Another problem is that the lawn mower cannot be continuously operated for a long period of time since the heat generated by the coils cannot be easily dissipated.